1. Field of the Invention
The present invention relates to pre-insulated piping systems, and more specifically to a method for countering the deleterious effects which can occur in the case of a breakdown of the piping insulation in the presence of water or other contaminants.
2. Description of the Prior Art
There are many instances in which insulated pipelines are needed. For example, distributed HVAC (heating, ventilation and air conditioning) applications utilize chilled water for cooling and steam or superheated water for heating. For convenience in the discussion which follows, steam and superheated water will be referred to collectively as “steam.” The chiller and boiler are typically contained in a central location and the chilled water and steam are distributed to other locations. For example, on a school or college campus, the chiller and boiler may be located in a power plant building. The chilled water and steam are distributed to classrooms in separate buildings.
A set of insulated pipelines is used to convey the chilled water from the chiller to other locations and back to the chiller. Another set of insulated pipelines is used to carry the steam from the boiler to the other locations and back to the boiler. The insulated pipelines are usually located underground.
Pre-insulated pipe is conventional and commercially available. There are predominately two types of such piping systems in use: Class-A drainable dryable testable (DDT); and polyurethane or polyisocyanurate “bonded” foam systems. Both of these systems use an inner “carrier pipe” to convey fluid. Although steel is the most commonly used material for the inner pipe which carries the media to be piped, copper or aluminum or other metals as well as fiberglass, PVC, and similar materials may be utilized, as well. Around the outside of the steel carrier pipe is a layer of insulating foam such as, for example, polyisocyanurate foam. Around the outside of the foam is a protective jacket of hard thermoplastic (such as high density polyethylene, HDPE). The foam has set up or cured within the outer jacket so as to bond to the jacket and to the inner pipe. The plastic jacket protects the foam from mechanical damage and also provides a water tight seal to prevent corrosion of the steel pipe. In the bonded type system, the foam and outer jacket, being bonded, do not move relative to the inner pipe. In the Class-A type system, on the other hand, the insulated inner pipe is designed to move independently of the associated outer jacket. In fact, there is an air gap between the inner pipe and outer carrier pipe in the class-A type system.
Despite the advances which have been made in pre-insulated piping systems in recent years, a need continues to exist for further improvements. For example, ground water is the enemy of all systems, but especially high temperature foam systems carrying fluids at over 212° F. The outer protective jacket of the insulated pipeline may, on occasion, be punctured or breached inadvertently as by maintenance or construction operations. This can occur where another utility line is being installed in the immediate vicinity, for example. If the outer protective jacket is penetrated for any reason, ground water and water vapor may enter the piping system and contact the inner carrier pipe, causing the water to boil. This boiling water attacks the outer foam insulation which surrounds the inner carrier pipe. This leads to deterioration of the foam and results in a bare pipe with huge energy loses, destruction of above ground grass, shrubbery, etc.
Perhaps even more commonly, the integrity of the pipeline is compromised because the installing contractor fails to properly install the seal at the joint location in the pipeline. Water then enters at the joint location and makes its way to the hot carrier pipe.
Problems are also exacerbated when pipeline maintenance personnel fail to act promptly to remedy breaches which have occurred in the surrounding insulation and protective jacket of the pipeline. Electrical monitoring systems will typically alert maintenance personnel to the fact that a leak exists. However, the maintenance staff may put off repairing the joint or other fault until, for example, the weather improves.
Pipe sections of the type under consideration are typically on the order of forty feet in length. As has been discussed, while a breach in the outer protective jacket can occur at any point along the length of piping, faults in the piping system most typically occur at the pipe ends where the connecting joints are located. When water penetrates the outer foam layer and contacts the hot inner metal carrier pipe, it starts to boil. The boiling water deteriorates the surrounding foam and can continue to travel for great lengths, eating up an entire pipeline.
Steps can be taken in an attempt to prevent external intrusion into the protective jacket of the insulated pipeline. For example, in the case of adjacent utility work, above ground markers, surveying tools, and the like can be used to help avoid contact with the underground insulated pipeline.
Additional training and education of the installing contractors and facility maintenance personnel can also help to prevent problems which lead to premature failure of the pipeline.
Despite attempts to prevent damage of the above type, however, there continues to exist a need for a system for mediating the effect of any breach or breakdown in the integrity of the outer protective jacket of such pre-insulated piping systems and in improving the integrity of the joint closures at the field joints in the piping system.
There continues to exist a need for such a system which would help to insure that any water which penetrates the outer jacket is prevented from boiling and traveling down the pipeline for any significant distance as a boiling liquid.